Fins used for scuba diving and snorkelling are well known. In particular, fins used in these activities have improved primarily in their design to reduce drag through water. The method of attaching fins to the feet of the diver or snorkeller, however, has not advanced to the same extent and such fins are still secured to the diver's feet by means of adjustable heel straps. Furthermore, divers now often wear diving boots of soft rubber over which their fins are worn. The difficulty of attaching and removing conventional fins on a pitching boat or diving platform presents a moderate difficulty which is further compounded if the diver is of a mature age or suffers from flexibility problems or has a bad back. Stooping or bending to release the heel straps of fins when also holding breathing apparatus or potentially hazardous implements such as spear guns can be particularly dangerous especially on a rocking boat. There is therefore a need for a fin design and a fin system for use with diving boots having a simplified attachment and quick release operation.